Siliceous compositions containing water soluble quinoid compounds as stabilizers



United States Patent ABSTRACT OF THE DISCLOSURE The evolution of gasfrom an aqueous dispersion of granular fused silica and colloidal si' raiL agp egus zinc-alkali metal silicate composition can be inhibi tedbyadding to the composition a small amount of a watersoluble quinoidcompound containing a. grouping selected from and .Mw

wherein X is selected from oxygen, sulfur, N-R, and salts of N-R, whereR is hydrogen, aliphatic or aromatic.

Cross reference to related applications This application is acontinuation-in-part of my pending application Ser. No. 369,616, filedMay 22, 1964, now abandoned.

Brief summary of the invention This invention relates to siliceouscompositions and more particularly is directed to stable aqueouscompositions containing granular, fused silica and colloidal silicauseful for producing heat resistant coatings on heat sensitive surfacesand also stable zinc-rich paints composed 'of zinc metal and alkalimetal silicates.

The compositions comprise the finely divided granular fused silicasuspended in colloidal silica aquaso'ls or the zinc metal-alkali metalsilicate mixtures both of which are stabilized against gaseous evolutionby the presence of small amounts of organic chemical compoundscontaining a quinoid grouping. Preferably, the fused silicacolloidalsilica compositions of the invention will also contain a suspendingagent, such as magnesium montmorillonite clay, to avoid sedimentation ofthe fused silica.

Detailed description of the invention The fused silica-colloidal silicacompositions of the present invention can be used for coating heatsensitive surfaces and are particularly useful for applying to surfaceswhich are coitacted by molten metals. In general, such surfaces will bethose which when contacted by molten metal are subjected to erosion orfracture. Illustrative of such surfaces are the inner walls of moldsused in' casting metal ingots, in particular ingots of ferrous metalsand the metal stools on which the molds rest during teeming. Alsosuitable for coating by these com positions are the surfaces of troughsand chutes used to transport molten metals, the interior surfaces ofladles, conveying recepacles, furnaces, and the like.

It is found that compositions containing finely divided granular fusedsilica suspended in colloidal silica aquaso'ls exhibit a marked tendencyto evolve excessive amounts of gases, particularly when subjected toelevated temperatures. Frequently, this gaseous evolution, which isprinci= pally hydrogen, is sufiicient to increase pressure in a fullcontainer such as a standard 55 gal. drum to as much as p.s.i. or higherwhich results in container ruptures and presents a serious safetyhazard. The mechanism responsible for this evolution of gases is notfully understood but is believed to be caused in some part by thereaction of elemental silicon present in the siliceous composition withalkali present therein from the colloidal silica aquasol component ofthe composition. It is to be understood that the invention is in no waylimited by the latter theory since regardless of what may be the causeof the gaseous evolution, it does commonly occur in siliceouscompositions of the type described and presents a serious problem to theart,

It has been found in accordance with the present invention that theabove-defined problem of gaseous evolution can be eliminated or greatlyminimized by the addition of small amounts of water-soluble compoundswhich contain the quinoid grouping wherein X is oxygen; sulfur; N-Rwhere R is hydrogen, aliphatic, or aromatic; or salts of said N-R group.

Illustrative of such compounds are quinones" such as p-quinone andp-quinone monoxi-me, Na sa'lt. Also illustrative are the followinganthraquinone dyes listed below with dye name, dye color index (0.1.)number, and structure given for each:

0.1. Dye Name No. Structure Acid Blue 25.. 62055 NH:

I -SOaNl-L Acid Dye 58100 HS 0 OH -SO:NB N8038- ll H!) 0 SH Acid Dye62530 SO3NB NaO S- SOaNB i G I Dye Name i No. Structure I Acid Dye 63605NaOaS-CHa-HN' NH-CHz-SO Na Acid Blue 4b 63010 Mordant Dye-. 63015 AcidViolet 42.... 62026 O NH;

-0 S0;Na l i i i I O- NH:

- C.I. Pigment Red 84.

Erweco Alizarlu Red SB. A

Also illustrative are the following thiazine dyes listed below with dyename, dye color index (0.1.) number, and structure given for each:

cxl

0.1. Dye Name No. Structure Mordant Dye" 52060 W l/\) oC2IIT- -S v X onU-S02Na Mgi'dant Blue 52055 J5 N (CH:)2N SUD Acid Dye 52035 HsCaN -S1IIC: s 112+ CH:

NaO|S l S0r Particularly preferred of these compounds are p-quinone;p-quinone monoxime, Na salt; Acid Blue 25, Cl. No. 62055; and Basic Blue9, Cl. No. 52015.

The granular fused silica suitable for these compositions has a silicacontent of not less than 97% silica as SiO and a thermal coefficient ofexpansion not greater than about 6 10-' cm./cm./ C. In preferred form,the compositions contain fused silicas which have the highest SiOcontent with the lowest coefiicient of expansion. Thus, a fused silicahaving a silica content of 97% and a coefficient of expansion from about5.5-6 l0-- cm./ cm./ C. is less desirable than a fused silica having asilica content of about 99.8% and a thermal coelficient of expansion nogreater than from about 4-5 l0'- cm./cm./ C. A fused silica of the typeuseful in the practice of the present invention has the followingtypical analysis:

Ingredients- Percent by weight SiO' 97.3 A1 0 1.7 Suboxides of silica0.55 Elemental silicon 0.45

A. material of this type has a thermal coefficient of ex-- pansion ofabout 5 X10 cm./cm./ C. Silica products of this type are readilyprepared by hammer-milling and grinding very pure fused silica glasseswhich are formed by reduction of relatively pure silica sands bygraphite electrodes in an electric arc furnace.

Silica aquasols suitable for use in. these compositions are described inBechtold and Snyder, U.S. Patent No. 2,574,902, Rule U.S. Patent No.2,577,485, and White U.S. Patent No. 2,285,477; Alexander U.S. PatentNo. 2,750,345, Marshall US. Patent No. 2,515,960, Trail U.S.

Patent No. 2.571%,743, Atkins '1' Patent. No. 3,012,973, and Legal US.Patent No. 2,724,701.

Such silica aquasols contain silica particles which are spherical andwhich have an average size from about 3 to 150 millimicrons. Preferablythe particle size is from about 5 to 50 millimicrons. The ratio Si0 :NaO can range from about 60:] up to the upper limits of the above citedpatents. In general, these sols will be basic in nature.

It is highly preferable, although not essential, to incorporate asuspending agent in these compositions to avoid the settling out of thefused silica particles. Very suitable suspending agents are themagnesium montmorillonite clays which are readily availablecommercially. Particularly preferred are themagnesium-aluminum-silicates having a lath-like structure which arecommonly known as hectorite-type clays such as the products Ben- A-Geland Ben-A-Gel, EW available from National Lead Company. These claysappear in electronmicrographs to have an ultimate particle which isabout one micron long 100 to 200 millimicrons wide and one tomillimicrons thick. Because the lath-like ultimate parti cles of suchclays occur in bundles, dispersal in water with ordinary mixing produceslittle viscosity increase even after prolonged contact with the waterand frequently sedimentation occurs on standing. To be most useful inthe compositions, for reasons explained hereafter, high shear mixing isemployed such as obtainable with a colloid mill. In this manner theaqueous siliceous compositions obtained are viscous and non-settling.

Because of the presence of the magnesium montmorillonite clay, thesilicious solids suspended within the aqueous dispersion remain insuspension -for extended periods of time. Thus, the compositions providefor the first time, a fused silica-colloidal silica aqueous compositionwhich can be pre-mixed well in advance of the time .for its intendeduse. In addition, the coatings resulting from spraying or brushing thesecompositions on heat sensitive surfaces obtain uniform thicknessthroughout whether the surface being coated is vertically orhorizontally disposed. The presence of the magnesium montmorilloniteclay prevents the tendency for the siliceous solids to concentrate atthe lower level of vertical or inclined surfaces. Another advantageresulting from the presence of the montmorillonite clay in thecompositions is that the solids in suspension do not clog the applyingequipment as for example, piping, spray nozzles, elbows, tees, rubberlines, etc. of pressurized spraying equipment used to apply thecomposition to surfaces.

The proportions of fused silica and colloidal silica in the coatingcompositions expressed on a solids weight basis can vary from 10:0.5 to10:60. Compositions in which the ratio of fused silica to colloidalsilica solids is about 10:3 are most preferred. The magnesiummontmorillonite clay, when used, is added in amounts ranging from 0.05to 2% by weight based on the aqueous fused silica-colloidal silicasuspension. The aqueous siliceous coating composition can have a totalsolids content ranging from about 30% to 80% by weight solids, with atotal solids of about 65% being most preferred.

The amount of the organic compound, containing the desired qninoidgrouping, required to provide eifective stabilization of thesecompositions is usually quite small and will vary to some extent withthe particular compound employed. In general, an amount ranging betweenabout 0.01% to 1% by weight based on the fused silicacolloidal silicaaqueous suspension will be desired, although some stabilization occurswhen lower concentrations are used. Amounts above 1% by weight can beused but usually are not justified economically. It is only necessary inusing amounts in excess of 1% by weight to insure that the stabilizingcompound does not have a tendency to gel the silica sol components ofthe composition. In most instances the preferred amount will rangebetween 0.1% and 0.6% by weight. The term water soluble used inconnection with the stabilizing compounds herein is intended to meanthose compounds containing qninoid grouping which are sufiiciently watersoluble to be dissolved in the fused silica-colloidal silica aqueoussuspension in an amount to provide some effective stabilization againstgaseous evolution which in view of the above discussion means compoundshaving a watersolubility in the compositions of at least about 0.01% byweight.

In formulating these compositions, the fused silica can be added to thecolloidal silica aquasol which contains the water-soluble stabilizingcompound and to which has previously been added with high shear mixingthe mag nesium montmorillonite clay. Alternatively, the fused silica andmontmorillonite clay can be premixed in a dry state and then added tothe stabilizing compound containing colloidal silica aquasol with highshear mixing. Also each of the ingredients of the composition can befirst suspended in aqueous medium and then the resulting aquasols can bemixed together in the proper proportions with agitation.

These compositions are most advantageously applied by spraying them uponthe surfaces to be coated with conventional spraying equipment.Alternatively, the composition can be applied by brushing, flow coating,dipping, or any other suitable means. It is preferred that thecompositions are sprayed upon surfaces which are at elevatedtemperatures to aid in driving off the aqueous carrier leaving behindthe granular fused silica bound together by colloidal silica particles.

The nascent hydrogen scavenger dyes of the invention can also be used toovercome the inherent problem of pinholing and blistering found inzinc-rich paints which results from the evolution of hydrogen gasresulting from the reaction of finely divided zinc metal with alkalimetal silicates.

Zinc-rich paints are coatings prepared from finely divided metallic zincand an alkali metal silicate. These coatings are used extensively forthe protection of iron and steel from corrosion. To use these coatings,zinc dust and silicate are stored and shipped separately due to thereaction of the zinc dust with the alkali silicates. Just before using,the two are mixed and applied to a sandblasted metal surface. The zincdust serves as a sacrificial anode being consumed rather than the basemetal.

Such coatings are described in detail in US. Patent 3,130,061. Thispatent also describes the problem of hydrogen gas evolution for thesepaint compositions.

The dyes of this invention have been found to eliminate the problem ofhydrogen evolution and as a result give coating surfaces with nopinholing, no blistering and improved hardness. Zinc dusts suitable foruse in this invention are those commercially available dusts which arepredominantly less than 15 microns in average particle size andpreferably those of 2 /2 to 5 microns average particle size.

Zinc dust should be used in amounts such that from to 96% of the dryfilm formed is zinc after the aqueous coating composition dries. Loweramounts of zinc can be used but performance suffers. In the case ofother metal coatings such as aluminum, amounts as low as 60% can beused.

In preparing the paint, zinc dust is admixed with the alkali silicatevehicle to give from about 0.9 to about 5 parts of zinc per part ofweight of silicate vehicle. Although larger amounts of zinc can be usedwith some silicate vehicles, practicality requires that zinc not exceedan amount which will give a paintable composition.

Zinc dust is the preferred metal. However, other metal 'pigments such asaluminum flake or finely divided lead can also be used in thesecompositions.

The finely divided inorganic additives traditionally used in paintcompositions can also be added with the zinc powder as desired. Forexample, pigments, extenders and further anti-corrosion agents can beadded for such ad-= vantages as they impart.

The silicate can be any alkali meiai silicate, such as 'odium,potassium. or lithium silicates. Combinations of these can also be usedsince it is quite popular to use a mixture of sodium and lithiumsilicates as the vehicle.

The concentration of the dye can be from 0.05 to 1% or even 3% based onthe weight of aqueous silicate binder solution. The high cost. of thedye will prevent one from using the higher concentration in practicaloperation. The preferred concentration is approximately 0.5% weight ofthe dye based on the weight of the alkali silicate solution used as thebinder.

A better understanding of the invention will be gained from thefollowing working examples:

EXAMPLE 1 A 300 gallon mixing kettle is charged with 500 lbs. ofcolloidal silica aquasol containing 30% by weight silica solids andhaving a SiO /Na o ratio of 96:1 (Ludox HS Colloidal Silica marketed byE. I. du Pont de Nemours & Co.). Four lbs. of Acid Blue 25, Cl. No.62055 are added to the colloidal silica aquasol with gentle agitation.

With vigorous agitation, 8 lbs. of magnesium montmorillonite clay(Ben-A-Gel, EW marketed by National Lead Company) are sifted into thesilica sol-dye mixture and agitation is continued until the clay ishomogeneously dispersed in the sol.

The resulting slurry is then recirculated for one hour through a threestage centrifugal pump, driven at 3450 r.p.m., to'shear the clay. As theclay slurry thickens due to the shear mixing, an additional 550 lbs. ofthe colloidal silica sol are added to keep the slurry fluid. When nofurther thickening due to shear mixing is observed, a

final amount of 900 lbs. of the colloidal silica sol is added withcontinued mixing to bring the total silica sol content added to 2000lbs., thus producing a highly sheared dispersion of 0.4% by weightmagnesium montmorillonite clay in the silica sol-dye mixture.

To this dispersion is then added slowly, with continued agitation, 2000lbs. of a fused silica powder of the following analysis SiO, percent byweight 97.3 A1303 1.7 Suboxides of silica do ..s 0.55 Elemental silicondo..- 0.45 Thermal coefiicient of expansion cm./cm./" (3.. 5X10- andhaving the following particle size distribution:

Percent of particles by weight Size-microns 150 12 75-450 Coating ofthis composition on the inner surfaces of steel casting molds and uppersurfaces of casting stools prior to metal pouring prevents welding ofthe cast ingots to the molds and stools and prevents mold and stool erosion. Thus, mold and stool life are substantially prolonged and ingotsare readily removed from their molds.

8 EXAMPLE 2 The composition of Example 1 is prepared as describedtherein, except that 0.5% Ben-A-Gel EW, montmorillonite clay is usedinstead of 0.2%, 20 lbs. of Basic Blue 9, Cl. No. 52015 dye is addedinstead of the four lbs. of Acid Blue 25, Q1. No. 62055 dye, and theadditions are made without shear mixing.

The resulting composition has substantially the same properties and usecharacteristics as described for that of Example 1.

EXAMPLE 3 A 300 gallon mixing kettle is charged with 550 lbs. ofcolloidal silica aquasol containing 30% by weight silica solids andhaving a SiO /Na O ratio of 285 (Lu dox LS Colloidal Silica marketed byE. I. du Pont de- Nemours 8: Co.) Four libs, of p-quinone are added tothe colloidal silica aquasol with gentle agitation.

With vigorous agitation, 8 lbs. of magnesium montmorillonite clay(Ben-A-Gel EW, marketed by National. Lead Company) are sifted into thesilica sol and p-quinone mixture and agitation is continued until theclay is homogeneously dispersed in the sol.

The resulting slurry is then recirculated for one hour through a threestage centrifugal pump, driven at 3450 r.p.m., to shear the clay. As theclay slurry thickens due to the shear mixing, an additional 550 lbs. ofthe colloidal silica sol are added to keep the slurry fiuid. When nofurther thickening due to shear mixing is observed, a final amount of900 lbs. of the colloidal silica sol is added with continued mixing tobring the total silica sol content added to 2000 lbs., thus producing ahighly sheared dispersion of 0.4% by weight magnesium montmorilloniteclay in the silica sol and p-quinone mixture.

To this dispersion is then added slowly, with continued agitation, 2000lbs. of a fused silica powder of the follow ing analysis:

Thermal coetficient of expansion cm./cm./ C.... 5 X 10* The resultingsilicious composition has a pH of 9.6 and contains by weight solids. Itis ready for use as a coating on heat sensitive surfaces by spraying,dipping, or brushing it thereon. The solids contained in the siliciouscomposition remain homogenously dispersed under both static andvibration storage. It is sufiiciently fluid to be pumped throughconventional metal and rubber piping without any clogging tendencies.

Under confined storage for a period of one month, the siliciouscomposition is found to be free of any gaseous evolution and free fromany build-up of pressure within its containers.

Coatings of this composition on the inner surfaces of steel castingmolds and upper surfaces of casting stools prior to metal pouringprevents welding of the case in= gots to the molds and stools andprevents mold and stool erosion. Thus, mold and stool life aresubstantially prolonged and ingots are readily removed from their molds.

EXAMPLE 4 Example 3 above is repeated using p-quinone monox ime, Na saltin place of p-quinone whereby a silicious composition is obtained havingsimilar properties and use characteristics to that described for thecomposition of Example PLE 5 An anthraquinone dye is introduced into alithium sili- 9 cate solution at a concentration of 0.5% by weight. Thedye is SOsNa H SH The lithium silicate has a SiO to Li O ratio of 4.8and a total solids concentration of The lithium silicate is..thenformulated into a zinc-rich paint vehicle by the addition of 0.1%Carbopolfl941, as a thickener and 0.05% K Cr O as a corrosion inhibitor.This vehicle is then mixed with zinc to obtain 93% zinc in the dry film.

The paint is sprayed on sand blasted mild steel panels and dried for 1,2, 4 and 24 hours. For comparison purposes similar paint is preparedwith the exception that no dye is added and these are also applied in asimilar manner to metal panels. Panels are then immersed in tap waterfor one hour after the drying times indicated above, and then redriedtwo hours and abraded for 100 cycles with a Taber abrader. Vehiclescontaining the anthraquinone dye have a marked increase in theresistance of the coating to wet abrasion.

In addition these same panels while immersed in tap water show nohydrogen bubbles evolving from the coating making the coating lessporous and less susceptible to leaching of the binder. All of the panelssprayed without the dye show hydrogen evolution, some pinholing, andblisters in the dried film. The dye also seems to markedly decrease thereaction of the zinc with the silicate and as a result the pot life orthe time required for the zinc dust- 'lithium silicate mixture toincrease in viscosity in which it can no longer be sprayed seemed to beconsiderably improved.

I claim:

1. In siliceous compositions selected from the group consisting of acomposition useful for coating heat-sensitive surfaces comprising anaqueous dispersion of granular fused silica and colloidal silica and anaqueous zincalkali metal silicate composition useful for inhibitingcorrosion of metal surfaces the improvement comprisin a water-solublequinoid compound containing a grouping selected from and wherein X isselected from oxygen; sulfur; N-R where R is selected from hydrogen,aliphatic groups and aromatic groups; and salts of said N-R group, saidquinoid compound being present in an amount sufiicient to inhibitevolution of gas from said composition.

2. In a siliceous composition useful for coating heatsensitive surfacescomprising an aqueous dispersion of granular fused silica and colloidalsilica, the improvement comprising a water-soluble quinoid compoundcontaining a grouping selected from wherein X is selected from oxygen;sulfur; N-R where R is selected from hydrogen, aliphatic groups andaromatic groups; and salts of said N-R group, said quinoid 3. Thecomposition of claim 2 wherein said amount of said quinoid compound isfrom 0.01% to 1% by weight based on the weight of said dispersion.

4. The composition of claim 2 wherein said amount of said quinoidcompound is from 0.1% to 0.6% by weight based on the weight of saiddispersion.

5. The composition of claim 2 wherein the ratio of said fused silica tosaid colloidal silica in said aqueous dispersion is from 10:05 to 10:60on a solids by weight basis.

6. The composition of claim 2 wherein the total solids content is from30% to by weight.

7. .The composition of claim 2 wherein said quinoid compound isp-quinone.

8. The composition of claim 2 wherein said quinoid compound is p-quinonemonoxime, sodium salt.

9. The composition of claim 2 wherein said quinoid compound is 10. Thecomposition of claim 2 wherein said quinoid compound is 11. In asiliceous composition useful for coating heat sensitive surfacescomprising an aqueous dispersion of granular fused silica and colloidalsilica and from 0.05

to 2.0% by weight, based on the weight of said disper} sion, of amagnesium montmorillonite clay, the improvement comprising awater-soluble quinoid compound containing a grouping selected fromwherein X is selected from oxygen; sulfur; N-R where R is selected fromhydrogen, aliphatic groups and aromatic groups; and salts of said N-Rgroup, said quinoid compound being present in an amount sufiicient toinhibit evolution of gas from said composition.

12. The composition of claim 11 wherein said amount of said quinoidcompound is from 0.01% to 1% by weight based on the weight of saiddispersion.

13. The composition of claim 11 wherein said amount of said quinoidcompound is from 0.1 to 0.6% by weight based on the weight of saiddispersion.

14. The composition of claim 13 wherein said quinoid and .compound isp-quinone.

15. The composition of claim 14 wherein the ratio of said fused silicato said colloidal silica in said aqueous dispersion is about 10:3 on asolids by weight basis.

16. The composition of claim 14 wherein the total solids content isabout 65% by weight.

17. The composition of claim 12 wherein said quinoid compound isp-quinone monoxime, sodium salt.

18. The composition of claim 12 wherein said quinoid compound is O NH:

sosNfl 19. The composition of claim 12 wherein said quinoid compound isand wherein X is selected from oxygen; sulfur; N-R where R is selectedfrom hydrogen, aliphatic groups and aromatic groups; and salts of saidN-R group, said quinoid compound 'being present in an amount sufficientto inhibit evolution of gas from said composition.

21. The composition of claim 20 wherein the alkali metal silicate islithium silicate.

22. The composition of claim 20 wherein said amount of quinoid compoundis from 0.05% to 1% by weight based on weight of aqueous alkali metalsilicate solution.

23. The composition of claim 2 wherein said amount of said quinoidcompound is from 0.01% to 1% by weight based on the'weight of saiddispersion, the ratio of said fused silica to said colloidal silica insaid aqueous dispersion is from 10:0.5 to 10:60 on a solids by weightbasis and the total solids content is from 30% to by weight.

24. The composition of claim 20 wherein said zinc metal comprises fromto 96% by weight of said composition exclusive of water.

25. The composition of claim 24 wherein said alkali metal silicate islithium silicate.

References Cited UNITED STATES PATENTS 3,102,038 8/1963 Fisher 106843,184,815 5/1965 Reuter 1175.3 3,231,537 1/1966 Fisher 106-14 JULIUSFROME, Primary Examiner.

THEODORE MORRIS, Assistant Examiner.

US. Cl. X.R.

